Button cell batteries generally include a casing provided with a cup and a lid respectively forming the positive and negative poles of the battery. Conventionally, button cell batteries are sealed with a preformed elastomer seal which is positioned between the cup and the lid. This elastomer seal provides galvanic isolation between the poles and forms a barrier between the electrolyte contained inside the battery and the external environment. Such an assembly is disclosed, for example, in GB Patent No 1566061.
This assembly with a preformed crimped seal has the drawback of occupying a significant amount of space which will restrict the active volume of the battery. Further, it requires a step of folding the upper portion of the cup onto the lid to compress the elastomer seal and thus ensure sealed closure of the button cell.
To reduce the space allocated to the sealing junction, an adhesive joint instead of the preformed elastomer seal is a promising solution, but which raises some technical issues. Indeed, it is necessary to guarantee that the adhesive adheres properly to the surfaces to be assembled, and generally, to guarantee the mechanical and chemical resistance of the bonded assembly over time. In this respect, particular attention must be paid to the choice of adhesive and to the bonding procedure when the two poles of the casing are assembled. Those skilled in the art will choose, in particular, adhesives having low curing temperatures to avoid damage to the separator arranged inside the active material in the casing. Thus, it is recommended not to go beyond 70° C., which limits the opportunity to choose the most suitable adhesive for ensuring the best mechanical and chemical resistance of the assembly. Then, when the casing is sealed by bonding, particular care must be taken to avoid contaminating the adhesive or the bonding surfaces with the electrolyte which is generally present inside the casing, which would compromise the adhesion of the adhesive to the bonding surfaces and hence the mechanical resistance of the assembly.